The sun is mighty, but modern climate change is caused by human activity | Fact check

Kate S. Petersen, USA TODAY
Updated ·6 min read
268

The claim: Post implies modern climate change is caused by the sun

A Jan. 18 Facebook post (direct link, archive link) shows an image of the sun and the solar system planets. The sun is labeled "THIS IS WHAT CONTROLS THE CLIMATE," while a comparatively tiny dot that appears to be Earth is labeled "YOU LIVE HERE."

Some commenters appeared to take the post as evidence that humans are not responsible for modern climate change.

"Oh - I thought it was my 1 litre Ford," wrote one such user.

Another user posted a gif of Greta Thunberg saying "How dare you!" a line from her highly publicized 2019 speech on climate change.

The image, which was posted to the Facebook group "Climate Con," was shared more than 600 times in a month.

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Our rating: Missing context

The implied claim is wrong. While the sun significantly impacts Earth's climate, it is not responsible for modern climate change. There is extensive evidence that greenhouse gas emissions by human activity are causing climate change.

Modern climate change is driven by CO2 emissions, not changes in the sun

There has not been a change in the state of the sun that could explain modern climate change, according to NASA.

"The sun can influence Earth’s climate, but it isn’t responsible for the warming trend we’ve seen over recent decades," the agency reports. "We know subtle changes in Earth’s orbit around the sun are responsible for the comings and goings of the ice ages. But the warming we’ve seen in recent decades is too rapid to be linked to changes in Earth’s orbit and too large to be caused by solar activity."

Since the late 1970s, researchers have been using satellites to track the amount of solar energy striking the Earth and have not detected an upward trend, according to NASA. However, the rate of global warming has accelerated significantly over this timeframe.

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In addition, if the sun was causing modern global warming, all layers of the atmosphere should be warming, NASA reports. But this is not what is happening.

Instead, the lower level of the atmosphere − the troposphere − is warming, while an upper level − the stratosphere − is cooling. This is partially because more heat is being retained in the troposphere due to greenhouse gases, such as CO2.

Greenhouse gases emitted by human activity are changing Earth's climate

While there is no evidence that modern climate change is caused by the sun, decades of research by generations of scientists have clearly demonstrated that it is caused by accumulating greenhouse gases emitted by human activity.

In the mid-1800s, scientists showed that greenhouse gases such as CO2 could slow the escape of heat into space. Researchers have since measured significant increases in global temperatures and atmospheric greenhouse gas levels.

"The amount of warming we see matches what we expect based on the increased CO2 we've added," Josh Willis, a NASA climate scientist, previously told USA TODAY. "The timing of the warming matches the timing of the CO2 increase caused by people. Not only that, the timing of global sea level rise matches the CO2 increase."

Global sea levels are rising because sea water expands as it warms, and additional water is being added to the ocean basins as glaciers and polar ice melt.

Additionally, because researchers have been publishing climate projections for decades, they've had the opportunity to test whether their understanding of greenhouse gas physics and planetary sciences holds up over time. Their models have been fairly accurate in predicting subsequent warming, according to an analysis by Harvard researchers and another by Carbon Brief.

Researchers can also tell that the excess CO2 causing the warming was emitted by humans. This is because atmospheric CO2 contains a disproportionate amount of the type of carbon found in fossil fuels and because the amount of excess CO2 in the atmosphere matches the amount released by human activity once other natural processes are taken into account.

"Scientists have looked for other sources of heat, cycles of the sun, volcanos on the sea floor and pretty much everything else you can think of," Willis said. "Nothing besides humans burning fossil fuels can explain all of these things."

USA TODAY reached out to the Facebook user who shared the post for comment but did not immediately receive a response.

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This article originally appeared on USA TODAY: Sun influences climate, but CO2 driving global warming | Fact check